Method of forming electromagnetic cores



1945. J. J. VIENNEAU 2,38?,99

METHOD OF FORMING ELECTROMAGNETIC CORE Filed Sept. 22, 1945 PRIOR ART F g-Z.

p/Q/O/i? ART Inventor; f Jacob J.\/ienneau,

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UNITED STATES PATENT OFFICE METHOD OF FORMING ELECTROMAGNETIC COREB Jacob J. Vienncau, Plttsileld, Mala, minor to General Electric Company, a corporation of New York Application September 22, 1943. Serial No. 503,402

3 Claims. (Cl. 29-15557) to form a coil of magnetic material suitable to produce a core and to a method of forming the core.

In my prior Patents 2,305,649 and 2,305,650, issued December 22, 1942, I have described and claimed an electromagnetic core and a method of forming the core which includes bendin fiatwise such as by winding a strip of magnetic material around a mandrel to form a coil of magnetic material which is suitable for use with assembly with a preformed coil winding to form an electromagnetic induction apparatus. As is described in these patents, the core is formed by first winding or bending the material fiatwise to form a coil of magnetic material, annealing, and then unwinding the coil and assembling with the coil winding without stressing the magnetic material beyond its elastic limit. The core after it is annealed may be assembled with the preformed coil winding by unwinding into a coil having a diameter larger than it has when annealed and then recoiling around the preformed coils so that the layers of magnetic material attain the same relative positions around the winding structure that they had when the magnetic coil was removed from the annealing oven.

As is described particularly in the specification of 2,305,649 beginning on page 3, in order that the coil may be unwound and wound around the winding leg of the preformed coil winding it is desirable to have a slight degree of looseness or spacing between layers at the ends or at corners of the core so that the layers at the long side may be in close contact so as to have the maximum space factor in the winding leg of the core. The patent then goes on to describe that this spacing may be accomplished by introducing shims between the layers or strip at the ends or short side. The patent further states that instead of using shims of magnetic material which drop out when the coil is unwound the spacing material may have a sufficiently low melting point as to run out during heat treatment or it may be loose powder.

I have found that when I space the successive layers of the coil at the end with a material which will burn or run out during the anneal as I do when employing spacers of metal, that the core at the looseend will be deformed in the annealing oven, since the force of gravity will cause the magnetic material at the annealing temperature, which is around 875 degrees C., to be deformed so that the loose end will not have a symmetrical shape when it is removed from the oven which is desirable to facilitate assembly with the conductive winding structure.

It is therefore an object of my invention to provide an improved method of forming a core for an electromagnetic induction apparatus when using a spacer material at the end which burns out or shrinks in the annealing oven which will allow the loose end of the core to be substantially symmetrical at the top and bottom when the core is removed from the annealing oven.

A further object of my invention is to provide an improved coil of magnetic strip material which is adapted for use as an electromagnetic core subsequent to a strain relief anneal.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing Fig. 1 illustrates an electromagnetic core made with looseness in one end thereof Fig. 2 illustrates a method of assembling the core with a preformed coil winding according to my above-mentioned patents; Fig. 3 illustrates an electromagnetic induction apparatus including the core and coil winding after assembly; Fig. 4 illustrates somewhat diagrammatically a coil of strip-wound magnetic material having one end spaced according to past practice and after it comes from the annealing oven; Fig. 5 ilustrates my improved method of inserting spacers in a coil during winding; Fig. 6 illustrates a coil with spacers ready to be put in annealing oven, and Fig. 7 illustrates an end of the core spaced according to my invention.

Referring particularly to Fig. 1 of the drawing I have illustrated a coil i0 of magnetic material which has been wound on a mandrel ii of suitable shape. The magnetic strip may be formed or bent around. the mandrel Ii in any suitable manner such as by spirally winding a magnetic strip on the mandrel ll while rotating the mandrel. After annealing the coil l0 at a suitable temperature which is about 875 degrees C. so as to remove all strain produced in the magnetic material during winding, the coil may be assembled with a preformed coil winding structure I2 in any suitable manner such as in the method shown in Fig. 2. Thus the outer end I8 is threaded through the winding window oi the preformed coil and then the coil of strip material is unwound around the winding leg II. The coil is then rewound in the a w. described in further detail in the above mentioned patents until the coil'of m netic material is mbled with the preformed coil winding so that the various layers of the core will have substantially the same relative positions that they did have when they were removed from the annealing oven, as is shown in Fig. 3.

In order to facilitate the assembly of the core with the preformed coil, metal shims is may be provided at one of the ends of the cofl of magnetic material, according to the teachings of my above mentioned patents. Thus when the core is assembled with the coil winding as is shown in Fig. 2, the shims will fall out, leaving a slight looseness oi' the core at one end so as to insure that after the core is assembled with the coil the various layers will assume the same position each had relative to the other after removal from the annealing oven and before unwinding.

As was mentioned in the above patent, particularly on page 3, column 2, line 27 and following, shims of metal or magnetic material may be employed, or a spacing material of a continuous strip which has a sufilciently low melting point to run out durin the anneal, or loose powder may be employed. Thus if the latter material can be employed and still produce a suitable core it will save the use of metal and also will save any handling of the shims during unwinding, as the material will burn out during the anneal. However, if a material which will burn out during the anneal is substituted for the metallic spacer it, when the coil is put in the oven with the winding leg is resting on a support ii, the spaced end is when the core is removed from the oven will have the non-symmetrical shape as is shown in-Fig. 4. Thus during the anneal a major portion of the paper will burn out and at the anneal temperature the magnetic material becomes relatively soft so that the force of gravity will cause the successive layers to move and thus build up at the lower corner it. It will be apparent that. a core withsuch a shape could not be efilciently assembled with a preformed coil.

In order therefore to employ a spacer material which will burn out during anneal and which will still produce a coil of magnetic material which has a substantially symmetrical loose end, I introduce suitable spacin strips 29 between the successive layers at one end, the strip progressingirom the inner periphery to the outer periphery at an angle with the longitudinal axis 2! of the core and mandrel in the manner illustrated in Fig. 5. Furthermore, these spacers are made of suitable material which will shrink sufficiently, or partially burn out so as to allow some sagging of the core in the annealing oven in a direction opposite to the build-up so as to produce not only a core which has suitable looseness at one end but which end is also substantially symmetrical. Thus the loose end of the core is built up oppositely from the position itwould assume it it were allowed to sag at the lower end as is shown in Fig; 4. Thus when the coil of magnetic material is assembled on a suitable base 22 for insertion in an annealing oven as 1:. illustrated in Fig. 6, the spacing strips 20 will progress from the inner periphery to the outer periphery at an angle with a horizontal axis 2! which angle may be any suitable amount so that after the coil of magnetic material is removed from the annealing oven the upper and lower corners at the loose end will be substantially symmetrical. 1 have found by experiment that'when asazose 1e mil magnetic strip material of about 3 per cent silicon is annealed in an oven for several hours at 875 degrees C. that the desirable angle for the spacers to progress is at about 30 degrees with the longitudinal axis 2i when a pap r spacer of about 11 mils and having a, width about equal to the width of the mandrel is employed. Under such conditions the,paper shrinks to about one-half its original size to allow a symmetrical loose end to obtain. It is to be understood, however, that the above data may be varied depending upon the type of material employed for the magnetic material, the type of material employed for the burnable spacers, and the temperature of the annealing oven, etc. Thus if a thicker paper is employed the sheets need not be the full width of the end of the mandrel. It will be seen that when the coil of magnetic material is placed on the base 22 to be put in the annealing oven, the leg it is placed downwardly so that the spacers progress upwardly. It is desirable to place the coil of magnetic material with the Winding leg i8 resting on a base so as to obtain the maximum space factor with that portion of the core which is the winding leg, which is placed through the coil window.

The shims 28 may be placed between the consecutive layers in any suitable manner, and as will be seen in Fig. 5 the mandrel l i has a pair of bars or arms 25 attached to the mandrel at the desirable angle at which the spacers are to progress from the inner periphery to the outer periphery. Thus as the mandrel ii rotates, the operator, at a convenient point each time the mandrel rotates around, can quickly insert a spacer between the successive layers using the arms as guides for the spacers.

. I have further found that with spacers which are employed in the manner described above that a convenient discernable line is produced at the corners which facilitates assembly of the core around the coil winding structure. Thus as is illustrated somewhat diagrammatically in Figs. 6 and '7 a discernable line is formed by the successive bends in the iron when it is bent over the edges of the spacers during winding, which bends do not entirely straighten out in the anneal, and'these bends may be employed by the operator in assembling the core around the coil winding so as to insure that the adjacent layers assembled with the preformed coil have substantially the same relative positions as they did have when the coil of magnetic material was removed from the annealing oven. The adjacent bends which in effect produce lines are shown as A-A before anneal in Fig. 6 and B-B after anneal in Fig. 7.

It has also been noted that the place where the core tends to bind is at the corners when assembling with the preformed coil winding, and thus the paper spacers when inserted in the manner described above produce a looseness at the corners of the end It so as to allow proper clearance at that part of the core.

Although I have shown and described particular embodiments of my invention, I do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:-

v1. A method of making acore for an electromagnetic induction apparatus including the steps of bending flatwise magnetic strip to form a noncircular core with a maximum dimension along a longitudinal axis, inserting spacers between successive layers of the strip'material at one end oi the core of material atleast a portion of which is burna'nle during subsequent annealing oi the core, the spacers being placed at the end oi the core so that they progress from the inner periphery to the outer periphery at an angle with the longitudinal axis, inserting in an oven to anheal the core with the longitudinal axis of the core being placed horizontal and with said spacers progressing upwardly,

2. A method of making a core for an electromagnetic induction apparatus including the steps oi" bending fiatwise magnetic strip to form a non circular core with a maximum dimension along longitudinal axis, inserting paper sheets be tween successive layers at one enri of the core and at an angle with the longitudinal axis, and plac= int; the core in an oven to he annealed. with the longitudinal axis horizontal. and with the s acers progressing upwardly so that during annealing the heat will at least partially burn out the paper and the force of gravity will cause the layers at the built up end to sag so as to be approximately symmetrical when the core is removed. from the oven.

3. A method or making a core for an electromagnetic induction apparatus including thesteps of winding a strip of magnetic material on. a rectangular shaped mandrel having maximum dimension along a longitudinal axis, placing spacing sheets of material shrinkable durin anheal between successive layers of the wound strip coil so that they progress at an angle with the longitudinal-axis oi the mandrel, and placing the coil and mandrel in an annealing oven with the longitudinal axis horizontal and the spacers progressing upwardly so that they will shrink and the force of gravity will. cause the encl to become substantially symmetrical.

JACOB J. VEENi TEL iU. 

